Thu·Mar 2, 2017Thursday·March 2, 2017

1. 01*

   Photon beam asymmetry $\Sigma$ for $\eta$ and ${\eta }^{\prime }$ photoproduction from the proton

   P. Collins🇺🇸 · B.G. Ritchie🇺🇸 · M. Dugger🇺🇸 · A. V. Anisovich🇩🇪 · M. Döring🇺🇸 · E. Klempt🇩🇪 · V. A. Nikonov🇩🇪 · D. Rönchen🇩🇪 · D. Sadasivan🇺🇸 · A. Sarantsev🇩🇪 · K.P. Adhikaria · Z. Akbar🇺🇸 and 131 other authors

   Measurements of the linearly-polarized photon beam asymmetry $\Sigma$ for photoproduction from the proton of $\eta$ and ${\eta }^{\prime }$ mesons are reported. A linearly-polarized tagged photon beam produced by coherent bremsstrahlung was incident on a cryogenic hydrogen target within the CEBAF Large Acceptance Spectrometer. Results are presented for the $\gamma p\to \eta p$ reaction for incident photon energies from 1.070 to 1.876 GeV, and from 1.516 to 1.836 GeV for the $\gamma p\to {\eta }^{\prime }p$ reaction. For $\gamma p\to \eta p$, the data reported here considerably extend the range of measurements to higher energies, and are consistent with the few previously published measurements for this observable near threshold. For $\gamma p\to {\eta }^{\prime }p$, the results obtained are consistent with the few previously published measurements for this observable near threshold, but also greatly expand the incident photon energy coverage for that reaction. Initial analysis of the data reported here with the Bonn-Gatchina model strengthens the evidence for four nucleon resonances -- the $N(1895)1/2^{-}$, $N(1900)3/2^{+}$, $N(2100)1/2^{+}$ and $N(2120)3/2^{-}$ resonances -- which presently lack the "four-star" status in the current Particle Data Group compilation, providing examples of how these new measurements help refine models of the photoproduction process.

   nucl-exPLB(2017)·53 citations
2. 02*

   Photons from the Early Stages of Relativistic Heavy Ion Collisions

   L. Oliva🇮🇹 · M. Ruggieri🇨🇳 · S. Plumari🇮🇹 · F. Scardina🇮🇹 · G. X. Peng🇨🇳 · V. Greco🇮🇹

   We present results about photons production in relativistic heavy ion collisions. The main novelty of our study is the calculation of the contribution of the early stage photons to the photon spectrum. The initial stage is modeled by an ensemble of classical gluon fields which decay to a quark-gluon plasma via the Schwinger mechanism, and the evolution of the system is studied by coupling classical field equations to relativistic kinetic theory; photons production is then computed by including the pertinent collision processes into the collision integral. We find that the contribution of the early stage photons to the direct photon spectrum is substantial for $p_T\approx 2$ GeV and higher, the exact value depending on the collision energy; therefore we identify this part of the photon spectrum as the sign of the early stage. Moreover, the amount of photons produced during the early stage is not negligible with respect to those produced by a thermalized quark-gluon plasma: we support the idea that there is no dark age in relativistic heavy ion collisions.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2017)·27 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.